If you are already know your way in OpenGL and want to do it the "recommended way":

Send matrix in "shader mode" by creating an ortho matrix :

Matrix4.CreateOrthographic(width, height, 0f, 1f, out projMatrix);

and sending it to your shader by calling

GL.UniformMatrix4(location, 1, false, projMatrix); //

Judging by the nature of your question i recommend going with first option first. The second method involves many more steps than what is shown. I only put it here so that you know what can be done. If you want a book or two i recommend: The OpenGL Programming Guide 7th edition. And OpenGL Superbible 5th edition.